Diamond has many outstanding properties such as high hardness and high thermal conductivity, and additionally high light transmittance and wide bandgap. Diamond is therefore used widely as a material for: various tools including cutting tools such as drill, end mill, milling machine, cutter, and tool bit and abrasion-resistant tools such as die, jet nozzle for water or other fluids, and stichel; optics such as window and lens; semiconductor; and electronic components such as heat dissipation substrate. It is considered that diamond will become still more important in the future.
Recently, the vapor phase synthesis method (hereinafter also referred to as CVD (Chemical Vapor Deposition) method) has enabled formation of a synthetic diamond having a relatively large area, such as approximately six inches in diameter in the case of microwave-assisted plasma CVD method, and approximately 30 cm×30 cm in the case of hot filament CVD method. However, the vapor phase synthesis method grows a synthetic diamond on a substrate, and therefore, for applications which require only the diamond, it is necessary to remove the substrate and thereby extract only the diamond. In the case where a different-kind substrate made of a material different from diamond is used, diamond may be removed by the following method. Namely, a solution with which the different-kind substrate chemically reacts is used to dissolve the substrate and thereby extract only the diamond. This method makes use of the fact that diamond does not react with and is therefore not dissolved in most solutions. In contrast, in the case where monocrystalline or polycrystalline diamond is used for the substrate, special methods are required as described in the following.
Japanese Patent Laying-Open No. 6-234595 (PTD 1) discloses a method according to which the vapor phase synthesis method is used to alternately deposit a first diamond layer with high optical transparency and a second diamond layer with low optical transparency and thereby form a multilayer stack, and laser light is applied to the multilayer stack to allow the second diamond layer to absorb the laser light and thereby cause the first diamond layer to be separated as a diamond thin plate.
Japanese Patent Laying-Open No. 2007-112637 (PTD 2) discloses a method according to which the vapor phase synthesis method is used to grow, on a substrate, a first diamond layer with low optical transparency and a second diamond layer with high optical transparency and thereby obtain a multilayer stack, laser light is applied from the upper side or the lower side of the multilayer stack to transform the first diamond layer, and the transformed first diamond layer is subjected to treatment such as heat treatment, electrochemical etching, or acid etching and accordingly removed, to thereby separate the second diamond layer.
U.S. Pat. No. 5,587,210 (PTD 3) discloses a method according to which ions are implanted into a diamond substrate to form a damaged layer of non-diamond carbon in the substrate, thereafter diamond is grown on the substrate by the vapor phase synthesis method, and thereafter the damaged layer is electrochemically etched to separate the grown diamond from the substrate.
Japanese Patent Laying-Open No. 2011-060860 (PTD 4) discloses a method of slicing a substrate, according to which laser light is applied to a surface of the substrate to form a reformed layer in the substrate, and thereafter the reformed layer is etched to slice the substrate.
Japanese Patent Laying-Open No. 2012-169363 (PTD 5) discloses a method of treating a substrate, according to which laser light is applied to a surface of the substrate to form a reformed layer in the substrate, and thereafter the substrate is divided at the reformed layer or in the vicinity of the reformed layer.
Japanese Patent Laying-Open No. 2011-060862 (PTD 6) discloses a method of slicing a substrate, according to which laser light is applied to a surface of the substrate to form a reformed layer in the substrate, thereafter a groove is formed in the reformed layer, and the substrate is removed along the groove.